Digital signal reproducing apparatus

1. A digital signal reproducing apparatus comprising: differential system equalizing means for outputting an equalized signal of a differential system by equalizing an input signal with respect to an equalizing reference of said differential system; integrating system equalizing means for outputting an equalized signal of an integrating system by equalizing said input signal with respect to an equalizing reference of said integrating system; adding means for adding the equalized signals of said differential system and said integrating system in a weighted manner to output an added equalized signal; and maximum likelihood decoding means for subjecting said added equalized signal to maximum likelihood decoding in order to output a discriminated binary result corresponding to said input signal.

2. A digital signal reproducing apparatus according to claim 1 , wherein said maximum likelihood decoding means includes: provisional discriminating means for provisionally discriminating one signal out of said added equalized signal and the equalized signals of said integrating system and said differential system in a predetermined sampling cycle so as to output a binary signal having a variable point, said variable point being either the same as or delayed by one clock cycle relative to a correctly discriminated result; and judging means for limiting, based on said binary signal, transitions of possible states which may be taken by said added equalized signal, and for detecting the most likelihood state of the transitions thus limited, thereby outputting said discriminated binary result.

3. A digital signal reproducing apparatus comprising: differential system equalizing means for outputting an equalized signal of a differential system by equalizing an input signal with respect to an equalizing reference of said differential system; integrating system equalizing means for outputting an equalized signal of an integrating system by equalizing said input signal with respect to an equalizing reference of said integrating system; differential system metric calculating means for calculating metric between said differential system equalized signal and a differential system amplitude reference value, said differential system amplitude reference value being taken by said differential system equalized signal, in a transition taken by said differential system equalized signal; integrating system metric calculating means for calculating metric between said integrating system equalized signal and integrating system amplitude reference value, said integrating system amplitude reference value being taken by said integrating system equalized signal, in a transition taken by said integrating system equalized signal; adding means for performing an adding process of the metrics of said differential and said integrating system for each of the transitions corresponding thereto using a predetermined weighting factor in order to output an overall metric of each transition; accumulative adding means for accumulating the overall metrics to detect likelihood of each transition; and judging means for judging the most likelihood of the one of each of said transitions and for outputting an accordingly discriminated binary value corresponding to said input signal.

4. A digital signal reproducing apparatus according to claim 3 , wherein said differential system metric calculating means discriminates provisionally the equalized signals of said integrating system and said differential system in a predetermined sampling cycle so as to output a binary signal having a variable point, said variable point being either the same as or delayed by one clock cycle relative to a correctly discriminated result; and wherein said differential system metric calculating means limits, based on said binary signal, transitions of the states taken by said differential system equalized signal, in order to calculate the metric for said differential system.

5. A digital signal reproducing apparatus according to claim 3 , wherein, when the transition of said integrating system reaches a predetermined equalizing reference value, said adding means replaces the weighted addition with a process in which the metric of said integrating system corresponding to said transition of equalizing reference value is added selectively in a predetermined ratio to the metric of the corresponding differential system.

6. A digital signal reproducing apparatus according to claim 4 , wherein, when the transition of said integrating system reaches a predetermined equalizing reference value, said adding means replaces the weighted addition with a process in which the metric of said integrating system corresponding to said transition of equalizing reference value is added selectively in a predetermined ratio to the metric of the corresponding differential system.

7. A digital signal reproducing apparatus according to claim 3 , further comprising level fluctuation detecting means for outputting a detected result of level fluctuations of said input signal, wherein said adding means varies said weighting factor in accordance with said detected result of level fluctuations.

8. A digital signal reproducing apparatus according to claim 4 , further comprising level fluctuation detecting means for outputting a detected result of level fluctuations of said input signal, wherein said adding means varies said weighting factor in accordance with said detected result of level fluctuations.

9. A digital signal reproducing apparatus according to claim 5 , further comprising level fluctuation detecting means for outputting a detected result of level fluctuations of said input signal, wherein said adding means varies said weighting factor in accordance with said detected result of level fluctuations.

10. A digital signal reproducing apparatus according to claim 6 , further comprising level fluctuation detecting means for outputting a detected result of level fluctuations of said input signal, wherein said adding means varies said weighting factor in accordance with said detected result of level fluctuations.